Wind turbines are commonly used to convert kinetic energy of an air stream into electric energy. An essential part of a wind turbine is the rotor with its rotor blades, which captures the kinetic energy and converts it into rotational energy. The efficiency of uptake of kinetic energy mainly depends on the aerodynamic profile and the pitch angle of the rotor blades. In order to adjust the pitch angle, the rotor blades, which are rotatably mounted to the rotor's hub by a pitch bearing, can be rotated around their longitudinal axis by using a pitch drive.
At very high wind speeds, the power captured from the wind by the rotor may exceed the limits set by the wind turbine's structural strength. Additionally, the generator's allowable maximum power constitutes a limit for the rotor's output power. Further, varying wind speed leads to a non-uniform rotation of the rotor and thereby creating additional non-uniform load. It is therefore a desire to constantly control power capture of the rotor and to maintain the rotor at uniform rotational speed. By far the most effective way is mechanical adjustment of the rotor blades pitch angle. In general, the rotor blades are turned with the aid of actively controlled pitch drives. Typically, each rotor blade has its own pitch drive to allow an individual adjustment of the pitch angle. Consequently, for controlling the pitch drives, a separate power control module is assigned to each pitch drive.
The set-up of a blade pitch control system outlined so far allows an instant reaction to varying wind conditions even during a gust of wind. The proper functioning of the blade pitch control system is essential for safe operation of a wind turbine. It is therefore a desire to ensure a constant and reliable control.